Sensor-driven lighting units monitor a characteristic of the environment with a sensor and utilize the sensor data to control the light source of the lighting unit. The most common example of sensor-driven lighting units are systems that monitor light levels using integrated photocells that measure ambient light levels. For example, night lights use ambient light to turn on when ambient light levels decrease and to turn off when ambient light levels increase. Similarly, smart street lighting uses detected ambient light to determine when to turn the light source on and off. Most often, the light level is monitored by a photocell directed towards the sky to observe the ambient light conditions. In which direction the photocell is directed, or which surface or area is utilized for light level monitoring, is driven primarily by product design. In most devices there is no relationship between the surface or area from which the ambient light level is monitored and the target surface to be illuminated.
Additionally, the photocell or photocells utilized in traditional sensor-driven lighting units cannot provide a spatial light distribution of an illuminated target surface. These systems, therefore, integrate all incoming detected light into a single value. As a result, the lighting unit can be adversely affected by light reflected from obstructions such as tree tops, objects moving through the light beam, and other physical obstacles that can, for example, cast shadows on or near the target surface. Accordingly, traditional sensor-driven lighting units provide sub-optimal light level monitoring, thereby resulting in poor system performance.
Accordingly, there is a continued need in the art for methods and systems that measure and characterize the illumination of a target surface within a lighting environment, in order to provide a more accurate light profile.